Hippocampal structure and function in individuals with bipolar disorder: a systematic review

Area of Science:

• Neuroscience
• Psychiatry
• Neuroimaging

Background:

• Bipolar disorder (BD) is associated with declarative memory deficits.
• The hippocampus plays a crucial role in declarative memory.
• Existing research suggests potential hippocampal abnormalities in BD patients.

Purpose of the Study:

• To systematically review structural and functional hippocampal abnormalities in bipolar disorder.
• To synthesize findings from studies comparing BD patients with healthy controls.

Main Methods:

• Systematic review of 25 studies (1043 patients) comparing BD patients and controls.
• Analysis focused on hippocampal structure (volume) and function using MRI/fMRI.
• Meta-analysis conducted on available volumetric data.

Main Results:

• A small but significant reduction in hippocampal volume was observed in BD patients compared to controls.
• Decreased hippocampal volume was noted in both adult and adolescent samples.
• Lithium treatment was associated with larger hippocampal volumes.
• Functional neuroimaging studies yielded contradictory results.

Conclusions:

• A modest reduction in hippocampal volume exists in BD, potentially greater in early-onset BD.
• Lithium may have a neuroprotective effect on hippocampal volume.
• The relationship between structural hippocampal changes and functional deficits in BD is largely undetermined.
• Further research, particularly on hippocampal function, is recommended for BD.